Control apparatus



June 16, 1936- F. H. GULLIKSEN CONTROL APPARATUS Filed Oct. 14, 1932 2Sheets-Sheet 1 WITNESSES:

INVENTOR H77 /7. GUM/f5 en.

ATTORNEY June 16', 1936. F, H GULUKSEN 2,044,164

CONTROL APPARATUS Filed Oct. 14, 1932 2 Sheets-Sheet 2 use 4k Twa/ I77WITNESSES: INVENTOR Ga/fi/fsen.

fivwfl/(gww/ Patented June 16, 1936 UNITED STATES 2,044,164 oomor.APPARATUS Finn H. Gii iiiksen, Wilkinsburg, Pa, assignor to WestinghouseElectric 8; Manufacturing Company, East Pittsburgh, Pa., a corporationct Pennsylvania Application October 14, 1932, Serial No. 637,771

8 Claims.

My invention relates to control apparatus and has particular relation toapparatus for controlling .the relative 'amount or the rate of depositof a constituent in a work substance.

It is an object of my invention to provide apparatus for so controllingthe relative amount of a constituent in a work substance that it shallbe maintained at a predetermined value and shall not vary alternately ina positive and negative sense from the predetermined value.

Another object of my invention is to provide apparatus for maintainingthe relative amount of a constituent in a work substance at apredetermined value in which certain elements of a type that shallrepress the tendency of the relative amount of the constituent to varyin a positive sense and in a negative sense about the predeterminedvalue. p

A further object of my invention is to provide apparatus for controllingthe relative amount of a constituent in a work substance, by theoperation of which a compensating variation in the relative amount ofsaid constituent shall be introduced when a variation from apredetermined value is detected and after the compensating variation isintroduced a predetermined interval of time shall elapse before thecompensating elements of the apparatus areagain responsive to thedetecting elements to introduce a further compensating variation.

An incidental object 01' my invention is to provide a novel system forselectively amplifying the output of a normally balanced network when itis in unbalanced condition in accordance with the polarity of theunbalance of. the network.

A further incidental object of my invention is to provide a simpleelectrical circuit for delaying the actuation of a switch apredetermined interval of time after an initial impulse has beenreceived.

A further incidental object of my invention is to provide a system fortiming the happening of a plurality of successive events that are auto-'matically to take place after the happening of a predetermined event.

More concisely stated, it is an object of myth vention to provide asystem for accurately and with certainty controlling the relative amountof a constituent in a work substance.

In accordance with my invention a photosensitive device is subjected tothe influence of a properly treated sample of the work substance, thecondition of which is to be regulated. A second photo-sensitive deviceis subjected to the influence of a standard which corresponds to thecondition at which the work substance is to be maintained. When thecondition of the work substance with regard to the particularconstituent which is being controlled varies from the desired normalvalue, the change thus produced in the two-photo-sensltive devices isproperly amplifled and the output of the amplifier is fed through theexciting coil of a relay of proper character which initiates thecompensating operation. a

In practice, my invention is generally applied to a system in which aconstituent is deposited in a container at a predetermined rate,together with the other elements of the work substance. To control therelative amount of the constituent its rate of deposit is varied. Thus,my invention has proved of considerable utility in the processing ofcopper ore. In one step of the treatment of the ore lime, copper ore andwater are continuously deposited in a container, the lime lendingcertain alkalinity to the mixture deposited. My invention has beenapplied to control the alkalinity of the mixture, and, in accordancewith my invention, the rate of deposit of the lime is varied toaccomplish this purpose.

Accordingly, if, in the above described'detecting operation a variationin the relative amount of the constituent is detected, the excitation ofthe initiating relay causes the control elements of the system to beoperated and to vary the amount of the constituent deposited. By theoperation of the initiatingrelay, the rate of deposit of the constituentis varied by a predetermined amount, and after the rate has attained thenew value, the variation in the rate is discontinued. The constituent isnow deposited in the container at the new rate and accordingly thecondition oi. the work substance should be changed with regard to theconstituent.

However, when the constituent is first deposited at the new rate, thechange does not at once take effect as far as the detecting apparatus isconcerned. An interval of time must of necessity elapse between thechange and the transmission of the change to the sample, that influencesthe photo-sensitive device. For this reason, the apparatus whereby therate of deposit of the constituent is varied and the detecting apparatusare uncoupled from each other for a. predetermined interval of timeafter the change in the rate oi deposit has been produced and the latterhas no influence on the operation of the former. After this interval oftime has elapsed, the two elements are again coupled together and therate-varying equipment is again subjected to the influences of thephoto-sensitive devices which, in turn, respond to any variations in thecharacter of the work substance.

It is seen that by thus delaying the influence oi the detecting systemon the compensating system the compensating system is prevented fromovershooting in its compensating effect and the relative amount of theconstituent in the work substance is maintained at a comparativelyconstant value.

The novel features that I consider characteristic of my invention areset forth with particularity in the appended claims. The inventionitself, however, both as to its organization and its method ofoperation, together with additional objects and advantages thereof willbest be understood from the following description of a specificembodiment when read in connection with the accompanying drawings, inwhich Fig. 1 and Fig. 1a constitute a complete diagrammatic view showingan embodiment of my invention.

As has been mentioned hereinabove, my invention has been applied withparticular success in the copper refining industry in which it isutilized tor the purpose of maintaining the alkalinity of a fluidcomprising copper ore, water and lime at a predetermined alkalinity. Theapparatus shown in the single flgurecomprises a tank I into which afluid comprising copper ore and water is fed through'an outlet 3 andinto which lime is fed by a cup conveyor 5. The cups 1 or the conveyor Idip into a tank 8 containing lime, are advanced to a point above thetank I containing the copper ore and water and there deposit the limeinto this mixture.

The conveyor 5 is motivated by a motor II which in turn is energizedfrom a generating system i3. The output 01' the generating system I3 andconsequently the speed of the motor Ii is controlled Irom a system ofrelays, the operation oi! which is dependent on the variation in thealkalinity of the fluid. Ii when a charge occurs the generating systemI3 is so modified that the speed of the motor It increases, the lime isdeposited at a greater rate than before the change has occurred and thealkalinity is correspondingly increased. (In the other hand, it thegenerator is so modified that the speed oi! the motor is decreased, thealkalinity oi the system is correspondingly decreased.

The mixture comprising the lime, copper and water which is deposited inthe tank l is, after being well stirred, removed from the tank i toanother tank (not shown) for iurther treatment through a tube I5 whichprojects into the tank I. The tube is equipped with a icy-pass pipe ilthrough which a small portion of the fluid is removed. This portion oithe fluid aimr being prop,- erly filtered and treated with a re-agent,such as phenolthalein, is projected through a transparent tube ii.

The transparent tube i 9 is disposed in the path of a radiant beamemanating from a source iii and the resultant beam transmitted throughthe tube i9 impinges on a photo-sensitive device 23. A secondphoto-sensitive device 25 is errorgized by radiations from the source 2ithat are transmitted through. a filter 2i which is of such color andcharacter, as to influence the photosensitive device 25 in a mannercorresponding to that in which it would-be influenced by a test sample01' the proper alkalinity.

The photo-sensitive devices 23 and 25 comprise the adjacent arms of abalanced network 29 oi! the type similar to a Wheatstone bridge. otherarms of the network 29 are properly subdivided portions 3i and 33 of aresistor 35 which is connected between the cathodes 31 and 39 ofphoto-sensitive devices 23 and 25. Potential is applied between thejunction points 4! and 43 oi. the resistor 36 and the cathodes 31 and 39from a suitable power source, the output of which is rectified andsuitably filtered.

The output terminals 45 and 47 of the bridge comprising the junctionpoints of the anodes 49 and the cathode 39 of the photo-sensitivedevices The 23 and 2! respectively and the other tap of the resistor IIare connected respectively to the control electrodes 33 and Ill 01 aplurality or high vacuum electric-discharge devices I51 and 59. Theanodes 8i and 63 of the devices 51 and 58 are connected to each otherthrough a variable tap potentiometer 85. The cathodes 61 and 88 a of thedevices 81 and 59 are energized from the secondary II oi a commontransformer 13 and are therefore substantially at a common potential.Plate potential is supplied-to the electric discharge devices 51 and 59from potentiometer "I8, the terminals 11 and 19 of which are connectedto the bus lines 8| and 83 01' a direct current power supply source (notshown). The midtap 85 of the potentiometer 15 is connected to the centertap 81 of the secondary ll of the transformer 13 whereby the cathodes B1and 69 oi the electric-discharge devices 51 and 59 are energized whileits lower terminal tap I1 is connected to the movable tap 89 or thepotentiometer "that is coupled between the anodes 6| and 63 of theelectric discharge devices.

When the alkalinity oi. the system varies from the predetermined valueat which it is desirable that it be maintained, the balance of thenetwork 29 in which the photo-sensitive devices 23 and 25 are connectedis disturbed and a potential, the polarity oi. which is dependent on thepolarity oi the variation oi the alkalinity, is impressed across theoutput terminals 45 and 41 of the bridge and, therefore, between thecontrol electrodes 53 and $5 of the electric-discharge devices ii! and59. Since the control electrodes 53 and 55 of the electric-dischargedevices 51 and 59 are connected to the cathodes 61 and 69 by the spacecurrent traversing the electrlc-discharge devices and since the cathodes61 and 69 are substantially at a common potential, the potential of onecontrol electrode 53 or 55 will be greater relative to its correspondingcathode 61 or 69 than the potential of the other control electroderelative to its cathode. A current of resultant magnitude and polarity,predetermined by the particular electric discharge device 5'! or 59, thecontrol elecrode of which. is at a greater potential relative to itscathode, will therefore be transmitted through the potentiometer 66 thatis connected between the anodes 6i and B3 of the electric-dischargedevices Ii'i and 59 and a drop ity and a magnitude predetermined by themagnitude and direction or the current, will be impressed across theterminals iii and 93 of a resistor that is coupled between the anodesiii and d3 of the electric-discharge devices 5i and lid in parallel withthe potentiometer B5.

The terminals 99 and 93 of the resistor 95 are connected respectively tothe control elecrodes 9i and 99 of a plurality of gas-filledelectrio-discharge devices Ill! and I03 through a plurality of suitablegrid resistors I05 and NH. The resistor 85 is moreover provided with acenter tap i0! which is connected to the movable tap N9 of anotherpotentiometer. One terminal I I2 01 the potentiometer i I I is in turnconnected to the center tap N3 of a section N5 of the secondary l H of atransformer I I9 whereby power is supplied to the gas-filledelectric-discharge devices lol and I03. The gas-filled devices arepreferably oi the hot cathode type and the section H5 0! the secondaryill, to the center tap II 3 of which the terminal H2 or thepotentiometer III is connected, is utilized for the purpose ofenergizing their cathodes HI and I23.

in potential of polar- The potentiometer III is moreover connectedacross a portion of the windings of another section I25 of the secondaryII1 of the transformer H9 and is thus energized. To one terminal I21 ofthe last-named section I25 of the secondary H1 a plurality of conductorsI23 and I3I are connected. One conductor I29 is connected to the anodeI33 of one electric discharge device Illl through a movable contactorI35 of a relay S31 and the exciting coil I39 of another relay Illi whilethe other conductor I3I is connected to the anode I43 of the otherelectric discharge 1 device I03 through a movable contactor I48 of thelastnamed. relay MI and through the exciting coil N1 of the first-namedrelay E31. Since an inter mediate tap I49 oi the section I25 of thesecondary I I1 is connected substantially to the cathodes IZI and I23 ofboth electric discharge devices I06 and I03, the relays I31 and Ill areenergized respectively through the electric discharge devices I03 and NHand through the movable con tactors I and I35. The relays I31 and MI aretherefore interlocked and when one electric discharge device lsenergized thev other must necessarily be deenergized.

Each of the gas filled electric-discharge devices l0I and I03 is of thetype having an energized condition and a deenerglzed condition and iscapable only of abrupt transition from one condition to the other. Thecondition in which an electric-discharge device of this type is at anyparticular time, is dependent on the potentials impressed between itscontrol electrode and its principal electrodes and between its principalelectrodes. Ii, while the device is in a deenergized condition, thepotential of the control electrode is so varied that it becomesenergized. the device remains energized until the potential between theprincipal electrode is reduced to a value below the ionizing potentialof the gas in the electric-discharge device regardless of furthervariations in the control potential.

In the present instance, both electric discharge devices WI and I03 aremaintained normally deenergized and when a potential impulse of propermagnitude is transmitted from the high vacuum electric-discharge devices51 and 59 and is impressed between the control electrodes 91 and 99 andthe cathodes HI and I23, one gasfilled electric-discharge device IM orI03, depending on the polarity of the impulse that is transmitted, isenergized and a current is transmitted through the exciting coil I39 orI41 of the corresponding relay I4I or I31. The magnitude of thepotential impulse for which either of the electric discharge devices IIor I03 becomes energized is regulated by the potentiometer III that isconnected to the cathodes I2I and I23 of I the electric dischargedevices.

The-relay l31 or MI is, therefore, energized and its movable co-ntactorI35 or I45, which is in series with the plate circuit of the otherelectricdischarge device II or I03 is disconnected from itscorresponding fixed contacts I5I or I53 and thus prevents the otherelectric-discharge device I03 or IIII from becoming energized by reasonof any transient effects which might be produced by drainage or thesupply of power from or to any part of the system.

For purposes of simplifying the explanation, let it be assumed that oneof the electric discharge devices I03 and its corresponding relay I31 isenergized. The upper movable 'contactor I55 of the relay I31 engages aplurality of corresponding fixed contacts I51 and a circuit is closedthrough the movable contactor I59 of a third relay I6I and through theexciting coil I03 of a 4th relay I55. The 4th relay I55 is locked in itsenergized condition through its central movable contact 191 and itsupper movable contactor I69 engages a. plurality of corresponding fixedcontacts III to close a circuit through the movable contactor I13 of a5th relay I15 and through the exciting coll I11 oi 6th relay I13.

The latter relay I19 being now energized, its movable contactor :lGIengages a plurality of fixed contacts I 83 to close a circuit through aportion I35 of the windings I51 of a split-winding motor I83, thusenergizing the motor to rotate in one direction. The shaft I9I oi themotor 189 is coupled to the movable contactor I93 of a rheostat I95. Themovable contactor M3 and a fixed terminal I91 of the rheos'tat I95 areconnected to the output terminals I99 of a pilot generator 20l energizedfrom the motor Ii whereby the cup conveyor 5 is driven and through theexciting coils 203 and 205 of the controlling relay 201 of the regulator209 whereby the output of the power supply generator I3 is regulated. Asthe excitation of the controlling relay 201 is varied by the impedancewhich is shunted across or serially connected to the exciting coil 2 I3oi the generator I 3 is dependent on the position of the movablecontactor 2I I.

As the output of the generator I3 is varied, the

speed of the motor II whereby the cup conveyor v5 is motivated is variedand the deposit of lime in the mixture 0! copper ore, water and lime isvaried to correspond to the indication of the photo-sensitive system,

To return now to the relay system, it is noted that the 4th relay I03 isin energized condition and that consequently its lower movable contactor2I5 is in engagement with its corresponding fixed contacts 2I1. Acircuit is, therefore, closed through contactor 2I5, a potentiometer2I9, the plate circuit of an electric-discharge device 22I of the highvacuum type and the exciting coil 223 of the 5th relay I15. A capacitor225 is connected between the movable top 221 of the last-mentionedpotentiometer 2I9 and the control electrode 229 of theelectric-discharge device 22I and a suitable resistor 23I is connectedbetween the lower terminal 233 of the potentiometer 2| 9 and the controlelectrode.

When the lower movable contactor 2I5 of the 4th relay engages itscorresponding fixed contacts 2", a small current is transmitted throughthe electric discharge device 22I which is, however, insuillcient toenergize the 5th relay I15. On the other hand, the capacitor 225 in thecontrol circuit of the electric-discharge device 22I ischargeol by thesmall current through the resistor 23I and through the potentiometer 2 I9 and, as long as the charging current flows through the resistor 23!,the control electrode 229 is maintained at a potential that is negativewith respect to the cathode 235. The output of the electric-dischargedevice 22I, therefore, increases at a rate dependent on the relativemagnitudes of the capacitor 225 and the resistor 23I and finally attainsa value that is sufficient for the excitation of the 5th relay I15. Inpractice, I have found that the 5th relay I15 should preferably beenergized, approximately one-hali second after the 4th relay I isenergized.

When the 5th relay becomes energized, its upper movable contactor H3 isdisengaged from its corresponding fixed contacts 231 and the circuitthrough the 6th relay I19 is opened. The latter relay drops out and,accordingly, the motor I89 whereby the rheostat 195 in the pilotgenerator circuit is varied is deenergized. At this time, a variation ofpredetermined magnitude has been applied to the generator l3 whereby thedriving motor ii is energized and the lime is being deposited in the oremixture at a rate corresponding to the latest speed of the motor.

However, since a considerable interval of time must elapse before theeffect 01' the variation in the speed is transmitted to the test samplein the tube I9, I have found it advisable to prevent the operation orthe compensating system for a predetermined interval oi time which, inpractice, is of the order of five minutes. This object is accomplishedby utilizing a second time delay relay of the thermionic type.

When the 5th relay H5 is energized, its lower movable contactor itsengages a plurality of fixed contacts 2 and a circuit is closed througha potentiometer 248. The terminal taps 245 and 2 5? of the potentiometer263 are connected to the bus lines at and 83 oi? the power source whileits central tap M9 is connected to the cathode 2M of a high vacuumelectric-discharge device 253. It is also connected to the controlelectrode 265 of the high vacuum device 253 through a resistor 25?. Acapacitor 255 is connected between the control electrode 255 of thedevice 253 and a movable tap it! of the potentiometer M3.

The electric-discharge device 263 is normally in deenergized conditionbut when the lower movable contactor 239 of the 5th relay engages itscorresponding fixed contacts 2i i, its principal circuit is closed. Atthe same time, a charging current is transmitted through the resistor251' to the capacitor 259 and a drop in potential is, therefore,impressed between the cathode 258 oi the elcctric olischarge device 253and its control electrode 255. The output of the electrlc-dischargedevice 253 is, therefore, maintained at' a lower level for an intervalor time determined by the relative magnitudes of the resistor 25 i andthe capacitor 259 in its control circuit. Aiter this interval of timehas elapsed, a comparatively large current is transmitted through theelectric-discharge device 253 and through the exciting coil 253 of thethird relay ltl, which is in series with its plate circuit.

When the third relay l6i is energized, its upper movable contactor l59becomes disengaged from a plurality of corresponding fixed contacts 265,the lock-in circuit through the 4th relay B65 is opened and the 4threlay is deenergized. At the same time, the lower movable contactor Billof the 3rd relay it! engages a plurality of corresponding fixed contacts269 and a circult is closed through the central movable contactor fillof the 5th relay, the lower movable contactor 261' of the 3rd relay, thetime-delay circuit associated with the first-mentioned time delaysystem, and the exciting coil 223 of the 5th relay H5. It is to be notedthat the central movable contactor 2 of the 5th relay "5 has replacedthe lower movable contactor 2&5 oi the 4th relay $5 in maintaining theabove-clescrlbed circuit closed for the reason that the 4th relay wasdeenergized when the third relay l6l was energized. The connectionsbetween the capacitor 225 and the terminals 8| and 83 of the powersource whereby it was charged are now reversed and the capacitor isquickly discharged and recharged to the opposite polarity. Theexcitation ol the electric-discharge device 22! associated with thefirst-mentioned time delay system is, therefore, reduced substantiallyto zero and the 5th relay I15 is deenergized reverting the whole systemto its initial condition and rendering the compensating elementsresponsive to the output of the balanced network.

It is to be noted that if the response of the balanced network 29 hadbeen such that the other interlocked relay MI had been energized insteadof the relay I31, the same series of steps would have been repeated withthe 4th and 6th relays Hi5 and H9 replaced by two relays 2'13 and 215 soconnected to the system as to cause the control motor E89 to rotate inthe opposite direction and the rate of deposit of lime to be varied inthe opposite sense.

While my invention has been shown herein as applied to a particularsystem, it is apparent that it should not be restricted in its scope tosuch a system. As is apparent from a consideration of the invention, itcan be applied in any contingency where it is desirable that therelative amount of a constituent in a work substance be maintained at apredetermined value or between pre determined limits. Thus, my inventionmay be applied with advantage in water treatment-to maintain thepercentage of chlorine in the water at a predetermined value. It mayalso be applied in numerous other fields which could be named withfacility.

Moreover, it is well to keep in mind that the specific elements andcircuits utilized in certain parts of this system, as it is shown, maybe replaced by other elements when any necessity therefor arises. Thus,the high vacuum electricdischarge devices 22i and 253 in the time delaysystems may be replaced by gas-filled devices or mercury-pool devices.Also, the hot cathode gasillled devices not and int that are connectedthrough the exciting coils iii?) and iii of the interlocked relays l4!and I3! may be replaced by mercury pool devices of similar nature. Incertain systems it may also be possible to eliminate one of the groupsof amplifying electric discharge devices.

Although I have shown and described certain specific embodiments of myinvention, 1 am fully aware that many modifications thereof arepossible. My invention, therefore, is not to be restricted exceptinsofar as is necessitated by the prior art and by the spirit of theappended claims.

I claim as my invention:

1. A system for controlling the relative amount of a constituent in awork substance comprising means to respond to variations in the relativeamount of said constituent in said work substance, means, to be actuatedby said responsive means when the relative amount oi said constituentvaries from a predetermined value, for applying a compensating variationin the relative amount of said constituent, the last said means beinglocked in in its operative condition and being operative after itsactuation irrespective of the condition of its actuating means, means,other than said locked-in means, for interrupting the application ofsaid compensating variation after a predetermined interval oi time andmeans, other than said locked-in means, to be actuated by saidinterrupting means, for preventing the application of anothercompensating variation until a second interval of time has elapsed toprovide for the proper influence of said first-named compensatingvariation on said responsive means.

2. A system for controlling the relative amount of a constituent in awork substance comprising means to respond to variations in the relativeamount of said constituent in said works substance, means, to beactuated by said responsive means when the relative amount of saidconstituent varies from a predetermined value, for applying acompensating variation in the relative amount of said constituent, thelast said means being locked in in its operative condition and beingoperative after its actuation, irrespective of the condition of itsactuating means, means, other than said locked-in means, forinterrupting the application of said compensating variation after apredetermined interval of time and means, other than said locked-inmeans, to be actuated by said interrupting means after said interval oftime for reverting said means for applying a compeneating variation to.a condition such that it is again responsive to said responsive meansonly after a second interval of time has elapsed thereby to provide forthe proper influence of said firstnamed compensating variation on saidresponsive means.

3. A system for controlling the relative amount oi? a constituent in awork substance comprising means to respond to variations in the relativeamount of said constituent in said work substance, means, to be actuatedby said responsive means when the relative amount of said constituentvaries from a predetermined value, for applying a compensating variationin the relative amount of said constituent, the last said means beinglocked in in its operative condition and being operative after itsactuation, irrespective of the condition of its actuating means, means,other than said locked-in means, for interrupting the application ofsaid compensating variation after a predetermined interval of time andmeans, other than said locked-in means, for both reverting said meansfor applying a compensating variation to its initial condition andreverting said interrupting means to a condition such that it is againresponsive to said responsive means only after a second interval of timehas elapsed thereby to provide for the proper influence of saidfirstnamed compensating variation on said responsive means.

4. A timing system comprising an electric discharge device, a timingcircuit to cooperate therewith, means for applying power to said timingcircuit and said electric discharge to increase the excitation of saidelectric discharge device at a rate predetermined by said timingcircuit, another electric discharge device, a timing circuit tocooperate therewith, means to be actuated by the output 01' saidfirst-named electric "discharge device when said output attains amaximum value for increasing the excitation of said last-named electricdischarge device at a rate predetermined by said timing circuit andmeans to be actuated by said last-named electric discharge device whenit attains its maximum excitation ior reverting the excitation of saidfirstnamed electric discharge device to its initial condition.

5. A timing system comprising an electric discharge device, a timingcircuit to cooperate therewith, means for applying power to said timingcircuit and saidelectric discharge to increase the excitation of saidelectric discharge device at a rate predetermined by said timingcircuit, another electric discharge device, a timingcircuit to co- 5operate therewith, means to be actuated by the output of saidfirst-named electric discharge device when said output attains a maximumvalue for increasing-the excitation of said last-named electricdischarge device at a rate predetermined by said timing circuit andmeans to. be actuated by said last-named electric discharge device whenit attains its maximum excitation for reverting the excitation of saidfirst-named electric discharge device to its initial condition and forrevetting said last-named electric discharge device to its initialcondition.

6. Apparatus for controlling the relative amount of a constituent in awork substance comprising means to respond to variations in the relativeamount of said constituent, means, to be actuated by said responsivemeans when the relative value for said constituent varies from apredetermined value, for applying a compensating variation, means,including an electric discharge device, a timing circuit to cooperatetherewith and means to cooperate with the compensating means to increasethe excitation of said electric-discharge device at a rate determined bysaid timing circuit, for interrupting the application of saidcompensating variation and means, including another electric dischargedevice, a time circuit to cooperate therewith and means to cooperatewith said interrupting means to increase the excitation of saidlast-named electric discharge device at a rate predetermined by saidlast-named timing circuit, for reverting said means for applying acompensating variation to a condition such that it is responsive to saidvariation-responsive means and for decreasing the excitation of saidfirst-named and said lastnamed electric discharge devices to theirinitial conditions.

7. A timing circuit comprising an electric discharge device having acontrol electrode and a plurality oi. principal electrodes, a networkcomprising a resistor and a capacitor coupled between said controlelectrode and one of said principal electrodes and means for energizingsaid electric discharge device to transmit a current for chargingsaidcapacitor through said resistor thereby to maintain a drop in potentialacross said capacitor and a resultant drop in potential between saidprincipal .electrode and said control electrode and to maintain theoutput of said device below a predetermined value until said capacitorhas been charged.

8. In combination with an electrical discharge device of a type having asubstantially unidirectional electrical conductivity and comprising ananode and a cathode and a control-electrode, a source of current supplyfor said device, a connection from one side of said source to saidanode, an impedance coupled between said cathode and saidcontrol-electrode, an impedance connected between said cathode to theother side or said source, and a capacitor connected between saidcontrol electrode and the last-mentioned impedance.

FINN H. GULLISEM

